Quinones are ubiquitous in nature and play an important role in electron transfer and energy transduction. Protein interactions modify the properties of these quinones so that the same quinone species can perform many functions in the cell. The bacterial photosynthetic reaction center is an excellent model system to study these quinone-protein interactions, since it contains two well characterized, chemically distinct quinone binding sites whose structures are known to atomic resolution. We are currently developing a genetic system in Rhodopseudomonas viridis to study these interactions. Protein engineering of the photosynthetic reaction center will be utilized to study quinone binding. An understanding of the molecular basis of quinone-protein interactions and how these interactions modify the chemical properties of quinones in the reaction center can be applied to other electron transfer and energy transducing systems, including those of mitochondria. This research project will promote biomedical research in the following ways: (1) Membrane-bound protein complexes are involved in many important biological processes, including respiration, transport processes, transformation, sensory transduction, receptor binding, and signal transduction. The reaction center is the only membrane protein whose structure is known to atomic resolution. Insights into the correlation of structure and function in this system can be applied to these other systems. (2) The study of the molecular basis of quinone function in reaction centers will provide the student with an understanding of the mechanisms of electron transfer in biological systems and substrate binding in enzymes. (3) The genetic engineering techniques and principles that will be used by the student in this proposal can be applied to a wide variety of other projects of biomedical relevance.